Myocyte hypertrophy in neonatal rat heart cultures and its regulation by serum and by catecholamines.

Abstract

SUMMARY. The role of hormones and other humoral factors in the regulation of myocardial hypertrophy has been difficult to evaluate. We asked whether myocardial cell hypertrophy could be demonstrated in cultures from the day-old rat ventricle and evaluated the effect of serum concentration and catecholamines on the growth process. Two single-cell preparations were used: serumsupplemented, bromodeoxyurdine-treated cultures and serum-free cultures with transferrin and insulin. Both preparations were characterized by myocardial cell predominance (about 75-80% of total cells) and constant cell numbers. Myocardial cell size was documented by photomicroscopy and quantified by volume (microscopic diameter of suspended cells), surface area (planimetry of attached cells), and total cell protein concentration (Lowry method and cell counts). Growth was also evaluated in pure nonmyocardial cell cultures. In cultures with 5% (vol/vol) serum, myocardial cell size increased 2-to 3-fold over 11 days in culture. Final volume, surface area, and protein concentration were about 3000 jum 3 /cell, 5000 /nmVcell, and 1500 pg/cell, respectively. Serum had a dose-related effect on myocardial cell hypertrophy; myocardial cell size increased about 4-fold when serum concentration was increased from 0% to 5% or 10%. Cells maintained in serum-free medium with transferrin and insulin (each 10 fig/ml) did not hypertrophy, but did remain responsive to the growth-promoting activity of serum. Chronic exposure to isoproterenol or norepinephrine (1 /IM) significantly stimulated myocardial cell hypertrophy. This stimulation was dose-related, was not blocked by equimolar propranolol, was not associated with a sustained chronotropic effect, and was more pronounced in the serum-free preparation. In pure cultures of nonproliferating (bromodeoxyuridine-treated) nonmyocardial cells, cell size also increased with time in culture, but variation in serum concentration and addition of norepinephrine had no significant effect on cell size. Myocardial cell hypertrophy occurs in culture and is regulated by variations in the culture medium, including serum, with its contained hormones and growth factors, and catecholamines. The culture preparation can be used to explore the regulation of myocardial cell hypertrophy by nonhemodynamic factors. (Ore Res 51: 787-801, 1982) VERY little is known about the role of hormones or other humoral factors in myocardial hypertrophy (Cohen, 1974). Experiments in vivo are complicated by hemodynamic, hormonal, and neural reflexes elicited by endocrine ablations or hormone treatments. In vitro models such as the isolated perfused heart or the heart in organ culture offer greater experimental control, but growth does not occur in these preparations (Morkin, 1974;Wildenthal et al., 1976). Cell cultures have been widely used to study the regulation of cell proliferation, and it has recently been proposed (Clark and Zak, 1981;Frelin, 1980;Speicher et al., 1981) that heart cells in primary culture may be a useful model system for stud...

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